1. Field of the Invention
The present invention relates to a method of growing diamond thin film, and more particularly to a method of growing diamond thin film on a heterogeneous substrate.
2. Description of the Prior Art
Diamond is considered ideal thermal dissipation materials and high frequency materials due to its high thermal conductivity. For example, it can be applied to high electron mobility transistors (HEMTs). A diamond film deposited on a heterogeneous substrate made of nitrides such as AlN/GaN or InAlN/GaN can act as a heat dissipation layer to transfer heat out of the electronic device. However, nitride substrates such as AlN or InAlN having fiat surface makes it difficult for diamond nucleation; this phenomenon has been reported in recent years. To solve this problem, rough surface of nitride substrate is usually formed by sputtering which provides more nucleation sites. Furthermore, it can be coordinated with scratching or seeding method to increase nucleation density. Nevertheless, it causes surface damage to the substrates, uneven distribution of nucleation sites, uneven thickness and rough surface of diamond films. These problems restrict industrial application of diamond.
According to conventional method of growing diamond thin film, a specimen of aluminum nitride is immersed into suspension fluid containing diamond powder for ultrasonic vibration for a period of time to generate scratches. Meanwhile, diamond powder is also embedded into scratches or absorbed on the surface of aluminum nitride to become nucleation sites. It could be seen that there is uneven distribution of diamond seeds and agglomeration of diamond power occurs on the surface of the specimen as shown in FIG. 2a. After pretreatments, a continuous diamond thin film is formed by microwave plasma chemical vapor deposition method (MPCVD). Results are shown in FIG. 2b and surface of diamond film appears cauliflower-like, which is rough and irregular.
If nucleation density of diamond on the heterogeneous substrate can be increased without damaging the substrate (e.g. group III-nitride substrate) and continuous diamond film with uniform thickness and high flatness can be further obtained, wide application of diamond can be achieved.